That is a bit odd. I don't have '/var/lib/tor/control_auth_cookie' It resides in /var/run/tor/control.authcookie
-rw-r----- 1 debian-tor debian-tor 32 /var/run/tor/control.authcookie
So read access should be possible.
If I remove this file, I also get [Errno 2] No such file or directory: '/var/run/tor/control.authcookie'
Does your user have read access to /var/run/tor?
Which version of arm you are using?
I use arm version 1.4.5.0 (released April 28, 2012)
Yes i also have this file and my user can access that one. But that is not the file arm tries to access apparently.
-rw-r----- 1 debian-tor debian-tor 32 Nov 3 19:05 /var/run/tor/control.authcookie
Same arm version:
arm version 1.4.5.0 (released April 28, 2012)